🇧🇾 Квант (Quantum): Part 4 (More Clock Rambling) [TCE #0467]
26More poking around the clock signal. To check if the shape of the clock signal could be okay, I compared it with the Парус ВИ-201 (Sail VI-201) that uses a similar circuit. Apart from the frequency being a little off, the shape looked pretty much the same.
Парус ВИ-201 (Sail VI-201): Part 1 [TCE #0415]
https://youtu.be/BXR9LQHF7KE
However it does seem that the "high" voltage level for the clock might be too low. As @skjerk pointed out earlier, the voltages around the board generally seem a bit low.
For the Z80 the minimum voltage of the "high" clock signal is Vcc - 0.6V. Checking the Vcc at pin 11 of the Z80 shows around 4.88V. This would mean our clock signal should hit at least 4.28V.
And it does not appear to, only hitting a max. of around 4V only and sometimes collapsing lower than that.
So could this be the problem? It is recommended to have a 330Ω pull-up resistor on the clock line ... we have a 1KΩ pull-up resistor and an electrolytic capacitor.
Not sure how to proceed - replace the pull-up resistor with a lower value, or replace the inverter and/or flip flop chips?
From Part 1:
Let's have a look at this Belarusian Sinclair ZX Spectrum clone called the КВАНТ (KVANT) or Quant(um) in English.
It's labelled "КВАНТ МИКРО ЗВМ" where ЗВМ is an abbreviation for "Электронная Вычислительная Машина" ... Electronic Calculating Machine ... so it's a "Quantum Micro Computer".
Lots of excellent information (in Russian), including documentation & circuit fixes:
https://zxbyte.ru/inter.htm